1. Field of the Invention
The present invention relates to a high tenacity polyester yarn with permanent low flammability, to processes for producing it and to its use for producing industrial textile and fiber materials.
2. Summary of the Invention
To produce industrial textile and fiber materials, for example high strength tarpaulins for textile constructions (e.g. self-supporting roofs, tents, guard and building fences), linear or sheetlike reinforcing materials (strength components) for the plastics and rubber industry (e.g. tire and drive belt cords, reinforcing layers for plastics-coated tarpaulins, roofing felts or conveyor belts, geotextiles) it is necessary to have polyester fiber materials which combine a particularly high strength with other properties specified for the specific use, for example certain values of the extensibility, of the shrinkage capacity or of the modulus of elasticity.
High strength/tenacity polyester fiber materials with such combinations of properties suitable for industrial use are known, for example from GB-A-1 174 101.
Commercial types for the industrial fields mentioned, for example the high strength polyester yarn types (R)TREVIRA HIGH TENACITY, have a tenacity within the range from about 70 to 85 cN/tex combined with a breaking extension within the range from 5 to 20% and a heat shrinkage at 200.degree. C. from about 2 to 22%.
Such high tenacity polyester yarns are generally produced by melt spinning relatively high molecular weight polyesters (IV&gt;0.8) at relatively low spinning take-off speeds and a subsequent, generally multistaged, drawing of the spun filaments to the required strength and breaking extension, optionally with application of a producer twist or twisting and a final heat-setting to stabilize the overall combination of properties. This conventional method of producing industrial polyester yarns is described for example in DE-C-12 88 734 (Chantry/Molini). More recent processes, for example the process described in EP-A-0 526 740 (Hoechst AG) for producing industrial polyester yarns, employ significantly higher spinning speeds and lower draw ratios.
Compared with industrial polyester yarns, polyester yarns for textile purposes have a distinctly lower strength level. The breaking strength of textile filaments ranges from about 30 to 50 cN/tex, and specific requirements, for example particularly low pilling, preferably requires types at the lower end of the strength range, in particular those having a particularly low transverse strength.
A requirement of polyester yarns and fabrics which was initially only demanded in the textile sector is low flammability.
To meet these requirements, it is known to provide the produced textile materials with flameproofing finishes. However, various auxiliaries used for this purpose are presently only on the surface of the textiles and are therefore relatively easy to remove, so that for example washing severely impairs the flameproofness.
A dramatic improvement in the flame resistance of polyester fiber materials was obtained by using polyester raw materials in their production which contained units in the chain of the polyester molecule which render the polyester itself low flammable.
Yarns made of such polyesters have a wash-resistant (permanent) low flammability.
Such modified low flammability polyester raw materials and fiber materials therefrom are known from German patents 2,346,787 and 2,454,189. The low flammability threads described there have a breaking strength of about 33 cN/tex and a breaking extension of 35% and consequently correspond to customary yarns for the textile sector. They are recommended in particular for the production of low flammability furnishings, carpets, curtains and the like.
A commercially available low flammability polyester filament yarn is for example (R)TREVIRA CS from Hoechst AG, which has a tenacity of up to about 45 cN/tex, which is relatively high for textile purposes, a breaking extension of about 30% and a dry heat shrinkage of about 20% at 200.degree. C.
As safety awareness increases, the demand for low flammability polyester fiber materials is increasingly also being voiced for the industrial sector. However, the experience of the last 20 years has shown that the chemical modification as known from the abovementioned references and for the production of textile polyester fiber materials (multifilament and staple fiber yarns and woven, knitted or nonwoven fabrics fabricated therefrom) has hitherto not been successful in the production of industrial fiber materials. This is because applying the processes for producing high tenacity industrial polyester yarns to the polyester raw materials known from the cited patent specifications does not produce the desired success but instead leads to appreciable losses especially in the tenacity.
It is also known to render polyesters low flammable by condensing halogen-containing units into the polyester chain.
According to EP-B-0 099 933, page 8, lines 60 ff, it is said to be possible to produce polyesters with a high modulus of elasticity (Young's modulus) which can be used as industrial reinforcing yarns in motor vehicle tires, conveyor belts and drive belts if .alpha.-.omega.-bis(2-chlorophenoxy)alkane-4,4'-dicarboxylic acids are used as dicarboxylic acid component in making the polyester. The yarn thus produced, however, naturally has the disadvantage common to all halogen-modified polyesters that thermal stress, for example the heat from the burning surroundings in the event of a fire, will cause it to eliminate appreciable quantities of hydrogen halide, which can lead to serious secondary consequences for property and persons.
So low flammability halogen-free polyester yarns were hitherto unavailable for typical industrial applications in which certain property profiles involving a high tenacity are required.
For some applications of industrial polyester yarns for which low flammability is required the only choice was therefore to finish the fiber materials subsequently with flameproofing agents with their abovementioned disadvantages, especially the only moderate washing, cleaning and weather resistance of the flameproofing effect.